Carotenoids direct solvent extraction

Carotenoids A large number of solvents have been used for extraction of carotenoids from vegetables matrices, such as acetone, tetrahydrofuran, n-hexane, pentane, ethanol, methanol, chloroform [427-431], or solvent mixtures such as dichloromethane/methanol, tetrahydrofuran/methanol, -hexane/acetone, or toluene or ethyl acetate [424,432-435], SPE has been used as an additional purification step by some authors [422,426], Supercritical fluid extraction (SEE) has been widely used, as an alternative method, also adding CO2 modifiers (such as methanol, ethanol, -hexane, water, methylene chloride) to increase extraction efficiency [436-438], In addition, saponification can be carried out, but a loss of the total carotenoid content has been observed and, furthermore, direct solvent extraction has been proved to be a valid alternative [439],... 

Procedures for the extraction of carotenoids from a wide variety of tissues have been reported in the literature. Because of differences in plant materials, no one method can be considered universal. However, the various methods are quite similar in principle. Carotenoids are extracted with an organic solvent such as methanol, ethanol, acetone, hexane, or petroleum ether. These may be used singly or as mixtures of two or more. In some cases, heating has been used to facilitate the extraction, although there is some risk in this as noted above. Grinding or blending has been used with some tissues, and in some cases this has been carried out with the solvent directly. When extracting fresh tissue, the initial extraction must be carried out with a water-miscible solvent such as acetone, methanol, or ethanol. Specific examples of procedures for various tissues are discussed in the review by Davies (1976). 

Alternatively, it is possible to inject the solvent extract directly for HPLC analysis. For good quantitation this method requires an internal standard or very careful measurement of liquid volumes. McClean et al. (69) and Nierenberg and Lester (70) used acetonitrile to denature plasma proteins and then solubilized retinol with ethyl acetate 1-butanol (1 1) for direct injection Siddiqui et al. precipitated proteins from serum by addition of acetonitrile, centrifuged, and then injected the supernatant (71). Retinoids and carotenoids can be efficiently extracted from one volume of serum or plasma with three volumes of 2-propanol dichloromethane (2 1) followed by centrifugation an aliquot can be directly analyzed by HPLC (72,73). The risks of sample loss and degradation during processing can thus be avoided. 

The extraction of chlorophylls and carotenoids from water-containing plant materials requires polar solvents, such as acetone, methanol, or ethanol, that can take up water. These extracts must then be transferred to a solvent such as diethyl ether in order to be stored stably. Samples with very high water content, such as juices and macerated plant material, are usually freeze-dried first, and can then be extracted directly with diethyl ether. After extraction, solutions are clarified and diluted to an appropriate volume to measure chlorophyll content by UV-VIS spectrophotometry. Absorption coefficients and equations needed for quantitative determination are given in unitf4.3. 

Water-containing plant materials need to be extracted with polar solvents such as acetone, methanol, or ethanol that can take up water. Freeze-dried plant tissues and freeze-dried juices can be directly extracted with diethyl ether, which contains traces of water and is more polar than light petrol or hexane. Pure light petrol or hexane are less suitable, because more polar pigments, such as Chi b or xantho-phylls, are only partially extracted from freeze-dried plant samples. A few drops of acetone or ethanol added to light petrol or hexane will, however, guarantee a complete extraction. This mixture will extract Chi a, Chi b, and all carotenoids—including xanthophyll esters and secondary carotenoids that are present in many fruits and juices—from the freeze-dried plant material. 

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